The present invention relates to a method of detecting an abnormality in a magnetic head, a circuit therefor, and a magnetic disk apparatus including an abnormality detection circuit.
A magnetic disk apparatus generally has additional functions of detecting operation abnormalities in respective parts inside the apparatus. One function is to detect an abnormality in a magnetic head for recording and reproducing data. The magnetic head is generally connected to a recording/reproduction integrated circuit through a plurality of thin wires. When such a wire is disconnected or short-circuited, occurrence of an abnormality in the magnetic head is detected.
An abnormality in the magnetic head is detected by monitoring a counter electromotive force generated across the two terminals of a recording coil in recording. More specifically, if the wire of the magnetic head is disconnected or short-circuited, detection is made not to generate the counter electromotive force across the two terminals of the recording coil. The detected record is stored in the recording/reproduction integrated circuit connected to the magnetic head in many cases.
FIG. 1 shows the configuration of a recording/reproduction integrated circuit connected to a magnetic head, and a circuit for detecting a recording abnormality, which are associated with the present invention. FIG. 2 shows the waveforms of respective signals used in this circuit. In FIG. 1, a constant-voltage power supply E1 of this circuit is connected between terminals T100 and T101. A magnetic head B1 has coils L1 and L2. One terminal of each of the coils L1 and L2 has a corresponding one of terminals T2 and T3. A terminal T1 connected to the terminal T100 is arranged at the connection node between the coils L1 and L2. The coils L1 and L2 are coupled with a coupling coefficient of 1.
A resistor RD connected between the terminals T2 and T3 is equivalent to a damping resistor for shaping the waveform of a recording current flowing through the coils L1 and L2 into a desired waveform.
A transistor Q1 having the collector and emitter connected between the terminal T2 and one terminal of a constant current source IW, and a transistor Q2 having the collector and emitter connected between the terminal T3 and one terminal of the constant current source IW correspond to driving transistors which receive the recording current through terminals T5 and T4 connected to their bases.
The terminals T2 and T3 are connected to the anodes of diodes D1 and D2 for detecting counter electromotive voltages generated on the positive sides of the terminals T2 and T3. A capacitor C1 and a constant current source I1 are series-connected between the terminals T100 and T101, while a capacitor C2 and a constant current source I2 are series-connected parallel thereto. One terminal of a biasing DC voltage source E2 is connected to the terminal T100, and the other terminal is connected to the emitters of transistors Q3 and Q4. A resistor R1 is connected between the collectors of the transistors Q3 and Q4 and the terminal T100. The bases of the transistors Q3 and Q4 are respectively connected to the anodes of the diodes D1 and D2, and correspond to transistors for detecting the counter electromotive voltages input through the diodes D1 and D2.
The constant current sources I1 and I2 correspond to current sources for removing accumulated electric charges in the capacitors C1 and C2, and the resistor R1 is a load resistor for the transistors Q3 and Q4. The connection node between the collectors of the transistors Q3 and Q4 and the resistor R1 is connected to a connection terminal T6.
The operation of the magnetic head abnormality detection circuit having this arrangement will be described.
When signals S1 and /S1 having complementary waveforms like the ones shown in FIG. 2 are respectively input to the terminals T4 and T5, a current from the constant current source IW alternately flows through the coils L1 and L2 of the magnetic head B1. At this time, voltages having counter electromotive voltage waveforms, shown as signals S2 and S3 in FIG. 2, are respectively generated at the terminals T2 and T3 of the magnetic head B1.
The diodes D1 and D2 extract the positive-side waveforms of the counter electromotive voltage waveforms of the signals S2 and S3, and supply them to the bases of the transistors Q3 and Q4. The bases of the transistors Q3 and Q4 are respectively connected to hold circuits each constituted by the capacitor C1 and the constant current source I1, or the capacitor C2 and the constant current source I2. With this arrangement, the peak voltages of the respective positive-side waveforms are held.
In FIG. 2, peak voltages VC of the signals S2 and S3 are indicated by broken lines, and held by the capacitors C1 and C2. While the counter electromotive voltage is generated across the terminals T2 and T3, i.e., the magnetic head B1 operates normally, the peak voltages VC are held by the capacitors C1 and C2, and the transistors Q3 and Q4 receiving the voltages VC through their bases are in an inoperative state. As a result, the potential of the resistor R1 connected to the collectors of the transistors Q3 and Q4 is held at a constant level.
If an abnormality occurs in the magnetic head B1, no counter electromotive voltage is generated across the terminals T2 and T3, the potentials of the capacitors C1 and C2 decrease due to the constant current sources I1 and I2, and the base potentials of the transistors Q3 and Q4 decrease. If the maximum voltage at the terminal T1 of the magnetic head B1 becomes lower than a potential EB, shown in FIG. 2, set at the voltage source E2, the transistors Q3 and Q4 are set in an operative state. Accordingly, the voltage of the resistor R1 rises to raise the level at the terminal T6. In this manner, when an abnormality occurs in the magnetic head, the abnormality is detected on the basis of the voltage generated at the terminal T6.
Most of magnetic heads used in magnetic disk apparatuses have been induction heads for both recording and reproduction. In recent years, however, the reproduction ability of the induction head is being limited, and the magnetic head is shifting to a magnetic head (to be referred to as an MR head hereinafter) using a magnetoresistive effect element for a reproduction head. This MR head is a combined head constituted by the induction head for recording and the magnetoresistive effect element (to be referred to as an MR element hereinafter) for reproduction. Therefore, the induction head and the MR head have no difference in terms of the recording ability. However, the data transfer rate is as high as, e.g., 100 Mbit/sec in proportion to the reproduction ability of the MR head, and the inductance is being decreased by decreasing the number of turns of the coil of the recording head in order to improve the leading characteristics of the recording current.
For example, the coil of a thin-film head as a kind of induction head has 40 to 50 turns. To the contrary, the coil of the recording head of the MR head has about 16 turns. Since the inductance of the coil is proportional to the square of the number of turns of the coil, it is obtained from the number of turns in the MR head. The inductance of the coil is proportional to the square of the number of turns of the coil, so that the inductance of the MR head is about 0.2 .mu.H.
In this manner, the magnetic head shifts from the induction head to the highly sensitive MR head, and the recording density increases to increase the data transfer rate. As a result, the inductance of the wire connecting the magnetic head and the recording/reproduction integrated circuit, and the presence of a stray capacitance cannot be ignored. Demand arises for highly precise detection of an abnormality in the magnetic head.
In most of recent magnetic heads, the recording coil is constituted by two terminals, so that the recording circuit and the magnetic head abnormality detection circuit are also indispensably improved.